Recently, a digital camera using an image sensor CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) is widely used. The digital camera is commercialized as a camera-only-product, and besides is mounted in a hand-held terminal such as a mobile phone or PDA.
However, the central processing unit of the hand-held terminal does not have as good a clock speed and memory capacity as that of a personal computer. And, development trends of the hand-held terminal move toward thickness and size reduction of the terminal. In this context, the terminal has a spatial limitation in mounting an additional device such as a camera. Further, there are limitations in applying various image processing techniques intended for a camera-only-product to a hand-held terminal, for example a digital image stabilization technique for preventing deterioration of a digital image caused by shaky hands of a photographer.
As well known, a digital camera supports an auto exposure mode. In the auto exposure mode, EV (Exposure Value) is automatically changed depending on luminance of a place to take a photograph. That is, EV is increased in a dark place and reduced in a bright place.
However, an increase in EV causes an increase in exposure time of the camera to a subject. In this case, an image blurring phenomenon occurs that a minute tweak of a focus caused by shaky hands is reflected on a photograph. To prevent the image blurring phenomenon, conventionally various image stabilization techniques were introduced, for example DIS (Digital Image Stabilization), EIS (Electrical Image Stabilization) or OIS (Optical Image Stabilization).
The DIS technique detects/compensates for a camera movement using an image signal stored in a memory. The DIS technique detects a movement vector using an image signal that is generated in an image pickup device and stored in a memory, and changes a read timing of the memory using the detected movement vector to compensate for a camera movement.
The DIS technique has an advantage of simple image stabilization. However, because a read timing of a memory is changed, a size of an image readable from the memory is equal to that of an effective pixel area. Thus, the DIS technique should expand an image read from the memory by digital zoom and play/record the expanded image, which results in deterioration of quality of an image.
The EIS technique detects/compensates for a camera movement using an angular velocity sensor and a high pixel image pickup device. The EIS technique detects the amount and direction of a camera movement using a horizontal/vertical angular velocity sensor, and changes an output timing of a high pixel image pickup device using the detected amount and direction of camera movement to compensate for the camera movement.
As an output timing of a high pixel image pickup device is changed, size of an image that is composed of an image signal output from the high pixel image pickup device is equal to that of an original image. This is because the high pixel image pickup device used in the EIS technique has more whole number of pixels than the number of effective pixels. Thus, the EIS technique can prevent deterioration of quality of the played/recorded image. However, the EIS technique requires an angular velocity sensor and a high pixel image pickup device, which results in an increase in manufacturing costs.
The OIS technique detects/compensates for a camera movement using an angular velocity sensor and a prism. The OIS technique is the same as the EIS technique in that the amount and direction of a camera movement is detected using a horizontal/vertical angular velocity sensor. However, there is a difference in that the OIS technique uses a prism capable of changing a path of light incident upon an image pickup device to compensate for a camera movement.
The OIS technique does not suffer deterioration of quality of the played/recorded image and does not require a high image pickup device. However, the OIS technique requires an angular velocity sensor and a prism, which increases the volume of a photographing device and manufacturing costs. Further, the OIS technique has difficulty in controlling the prism.